Macrophages were first identified in transparent starfish larvae (Astropecten pentacanthus) more than a century ago, so it is fitting that a new function for macrophages would again be discovered in transparent marine larvae, this time from zebra fish (Danio rerio). On page 1317 of this issue, Eom and Parichy (1) reveal a wholly unexpected tissue-specific function of macrophages—their cardinal role in long-distance communication between nonimmune cells. In doing so, macrophages choreograph the patterning of pigment cells that eventually form the stripes on zebrafish.
Author: Martin Guilliams
The most notable scientific milestone in photovoltaics in the past several years is the emergence of solar cells based on hybrid organic-inorganic perovskite materials. While conventional silicon and thin-film solar cells have seen steady improvements in their power-conversion efficiencies (PCEs) spanning several decades, hybrid perovskite solar cells have already reached a certified 22.1% PCE (1), matching conventional solar cell technologies in only a few years since their first device architecture was tested. Setting the stage for a disruptive technology in the field of photovoltaics is the seemingly winning combination of properties of hybrid perovskite materials: high absorption coefficient and a tunable energy band gap in wavelengths ideal for solar cells; long diffusion lengths and lifetimes for photogenerated charge carriers, which easily dissociate into efficiently collected electrons and holes; Earth-abundant elemental composition; and their compatibility with low-cost and low-temperature fabrication methods (2–5). On page 1288 of this issue, Blancon et al. (6) report on the observation of an enhanced photoresponse for layered perovskite materials. The results add, literally, a new dimension to the further development of high-performance perovskite solar cells.
Authors: Osman M. Bakr, Omar F. Mohammed
Molecular engineers have become increasingly adept at repurposing life's
building blocks to make custom self-assembled shapes. Because a single drop of
solution contains billions of such shapes, DNA origami smiley faces (1), RNA stars (2), and designer protein
polyhedra (3) may vastly
outnumber most other human-made objects on Earth. These shapes lack immediate
practical utility, but they transmit a powerful message: Researchers are
beginning to understand how molecules self-assemble. On page 1283 of this issue,
Praetorius and Dietz make another leap forward by demonstrating a novel class of
nanostructures, namely DNA-protein hybrid shapes (4). This is an important advance because it
provides a method to create human-designed shapes out of ingredients that are
generally compatible with living systems.
Author: Shawn M. Douglas
There are few sights more spectacular than the swarming of a school of fish or a
flock of birds that suddenly gives way to a directional motion. Arguably, our
admiration is rooted in the surprise that individual organisms, capable of
self-propulsion on their own, organize to move en masse in a coherent fashion.
Coherent motion is common in a large class of biological and synthetic materials
that are often referred to as active matter. Such materials consist of particles
immersed in a fluid that can extract energy from their surroundings (or internal
fuel) and convert it into directed motion. Living organisms, biological tissues,
rods on a vibrated plate, and self-phoretic colloids are just a few examples
(1). Similar to
schools of fish and flocks of birds, active matter often exhibits random
swarming motion (2–5) that until now was impossible to control or
use. On page 1284 of this issue, Wu et al. (6) demonstrate that an
active fluid can be manipulated to flow in a particular direction without any
external stimuli by confining it in microchannels.
Author: Alexander Morozov
Fire profoundly influences people, climate, and ecosystems (1). The impacts of this interaction are likely to grow, with climate models forecasting widespread increases in fire frequency and intensity because of rising global temperatures (2). However, the relationship between fire and biodiversity is complex (3, 4). Many plants and animals require fire for their survival, yet even in fire-prone ecosystems, some species and communities are highly sensitive to fire. Recent studies (2, 3, 5, 6) are helping to define fire regimes that support the conservation of species with different requirements in a rapidly changing world.
Authors: L. T. Kelly, L. Brotons
It is a human trait to search for explanations for catastrophic events and rule out mere “chance” or “bad luck.” When it comes to human cancer, the issue of natural causes versus bad luck was raised by Tomasetti and Vogelstein about 2 years ago (1). Their study, which was widely misinterpreted as saying that most cancers are due neither to genetic inheritance nor environmental factors but simply bad luck, sparked controversy. To date, a few hundred papers have been written in response, including (2–6), with some [e.g., (2)] coming to opposite conclusions. What is this controversy about? Tomasetti and Vogelstein concluded that 65% of the differences in the risk of certain cancers is linked to stem cell divisions in the various cancerous tissues examined (1). On page 1330 of this issue, Tomasetti et al. (7) provide further evidence that this is not specific to the United States.
Authors: Martin A. Nowak, Bartlomiej Waclaw
Like a lot of Hans Rosling's admirers, we discovered his work via his famous 2006 TED talk, “The Best Stats You've Ever Seen.” It was a mind-blowing speech (with more than 11 million views to date) with innovative graphics, good jokes, and a profound message: The world is getting better, and even some of the poorest countries are making progress. Hans was a showman, but he didn't sacrifice an ounce of complexity. He was—and this is a term of honor in our house—a data nerd. We sang his praises to just about anyone who would listen.
Authors: Bill Gates, Melinda Gates
Although the Paris Agreement's goals (1) are aligned with science (2) and can, in principle, be technically and economically achieved (3), alarming inconsistencies remain between science-based targets and national commitments. Despite progress during the 2016 Marrakech climate negotiations, long-term goals can be trumped by political short-termism. Following the Agreement, which became international law earlier than expected, several countries published mid-century decarbonization strategies, with more due soon. Model-based decarbonization assessments (4) and scenarios often struggle to capture transformative change and the dynamics associated with it: disruption, innovation, and nonlinear change in human behavior. For example, in just 2 years, China's coal use swung from 3.7% growth in 2013 to a decline of 3.7% in 2015 (5). To harness these dynamics and to calibrate for short-term realpolitik, we propose framing the decarbonization challenge in terms of a global decadal roadmap based on a simple heuristic—a “carbon law”—of halving gross anthropogenic carbon-dioxide (CO2) emissions every decade. Complemented by immediately instigated, scalable carbon removal and efforts to ramp down land-use CO2 emissions, this can lead to net-zero emissions around mid-century, a path necessary to limit warming to well below 2°C.
Authors: Johan Rockström, Owen Gaffney, Joeri Rogelj, Malte Meinshausen, Nebojsa Nakicenovic, Hans Joachim Schellnhuber
Make It Rain, Kristine Harper's detailed history of weather control in the United States, includes colorful details of cloud-seeding experiments, but the book is not so much about attempts to control the weather as it is about the political battles waged over the harnessing of the atmosphere: the control of weather control itself. Rather than revealing a history of what we might today call evidence-led policy, the book is a rogue's gallery of policy-led evidence, offering lessons about how science can be used as a tool of the state.
Author: Sarah Dry
Authors: Jorge L. Contreras, Jacob S. Sherkow
Authors: Eliécer E. Gutiérrez, Ronald H. Pine
Author: Beverly A. Purnell
Author: Leslie K. Ferrarelli